The atomic nuclei of certain materials possess magnetic moments which arise out of their inherent angular moments or spin properties. These special properties of certain materials form the principle upon which the nuclear gyro operates.
U.S. Pat. No. 3,778,700, assigned to the same assignee as the present invention, discloses an optically pumped nuclear magnetic resonance gyroscope device in the preferred embodiment of which two different isotopes of mercury are utilized in the cells of two interconnected spin generators. As taught therein, each spin generator comprises a mercury absorption cell containing .sup.199 Hg and .sup.201 Hg which is subjected to a DC magnetic field, H.sub.o and to an AC magnetic field, H.sub.1 perpendicular to field H.sub.o. The magnetic fields H.sub.o of the two cells are described as being equal and antiparallel to each other. The mercury absorption cells are optically pumped by a circularly polarized beam of light to increase the magnitude of the net magnetic moment and phase comparison means are provided to derive a readout signal representative of of gyro angular rotation about a given axis by comparing and phase outputs of the two spin generators.
The disadvantages of the prior art early schemes were:
1. Gyro output was in analog forms not readily useable by modern-day navigation computers without conversion.
2. Mechanization required bulky and expensive electro-mechanical devices which are slow in response time.
3. Stability of the phase shift introduced by the resolver scheme is dependent not only on the resolver characteristics, but also on the stability of the resistor and capacitor (the phase shifter works ideally only at a single frequency).
4. Filters prior to the resolver introduce phase instability with time degrading output.
Thus, there is a need to implement a system which will provide digital signals which will satisfy the fast mid-course corrections of present day missiles and other gyro controlled devices.